Using HMAC SHA256 in Ruby

Question

I'm trying to apply HMAC-SHA256 for generate a key for an Rest API.

I'm doing something like this:

def generateTransactionHash(stringToHash)
  key = '123'
  data = 'stringToHash'
  digest = OpenSSL::Digest.new('sha256')

  hmac = OpenSSL::HMAC.digest(digest, key, data)
  puts hmac
end

The output of this is always this: (if I put '12345' as parameter or 'HUSYED815X', I do get the same)

ۯw/{o���p�T����:��a�h��E|q

The API is not working because of this... Can some one help me with that?

Answer 1

According to the documentation OpenSSL::HMAC.digest

Returns the authentication code an instance represents as a binary string.

If you have a problem using that maybe you need a hex encoded form provided by OpenSSL::HMAC.hexdigest

Example

key = 'key'
data = 'The quick brown fox jumps over the lazy dog'
digest = OpenSSL::Digest.new('sha256')

OpenSSL::HMAC.digest(digest, key, data)
#=> "\xF7\xBC\x83\xF40S\x84$\xB12\x98\xE6\xAAo\xB1C\xEFMY\xA1IF\x17Y\x97G\x9D\xBC-\x1A<\xD8"

OpenSSL::HMAC.hexdigest(digest, key, data)
#=> "f7bc83f430538424b13298e6aa6fb143ef4d59a14946175997479dbc2d1a3cd8"

Answer 2

Try This:

hmac = OpenSSL::HMAC.hexdigest(OpenSSL::Digest.new('sha256'), key, data)

Answer 3

In my case (Ticketmatic) I had to create the HMAC like above and add an Authorization header to the request with the HMAC in it.

hmac = OpenSSL::HMAC.hexdigest(OpenSSL::Digest.new('sha256'), secret_key, access_key + name + time)
req = Net::HTTP::Get.new(uri)
req['Authorization'] = "TM-HMAC-SHA256 key=#{access_key} ts=#{time} sign=#{hmac}"
res = Net::HTTP.start(uri.hostname, uri.port, use_ssl: true) { |http| http.request(req) }

You can find a full gist here

And a blogpost with more explantion here